The present invention is drawn to an improved catalyst for use in the hydrodemetallization and hydroconversion of heavy hydrocarbon feedstocks and method of making same and, more particularly, an improved catalyst having two distinct phases supported on a refractory support wherein the first phase effectively stores metals removed from the feedstock and the second phase exhibits superior catalytic activity for hydrogenation when processing heavy hydrocarbon feedstocks.
Heretofore, operations such as hydrotreatment of heavy hydrocarbons are performed in the presence of catalysts comprising elements of Group VIII and Group VIB supported on a refractory oxide support. These types of catalysts suffer from a number of disadvantages. For example, during the hydrotreatment of heavy feedstocks the life of most of the conventional catalyst is shortened by a fast deactivation. The first cause for the deactivation is the deposition of coke on the catalyst. Coke deposits can be avoided by improving the hydrogenation activity of the catalyst. The second cause for the deactivation results from metal deposits on the catalyst.
Most of the patents related to improved demetallization catalysts deal with special designs of the catalyst pore size distribution. It has been found in the prior art that a catalyst having a macropore structure can generally accumulate higher amounts of metals. In order to achieve this macropore structure several approaches have been considered in the prior art. One of these is to vary the form and size of the catalyst particles and the surface area and the porosity of the catalyst support. The following patents are examples: U.S. Pat. No. 4,014,821, U.S. Pat. No. 4,082,695, U.S. Pat. No. 4,102,822, U.S. Pat. No. 4,297,242, U.S. Pat. No. 4,328,127, U.S. Pat. No. 4,351,717, U.S. Pat. No. 4,411,771, U.S. Pat. No. 4,414,141. The optimum pore structure appears to be well known in the previous art. Having established the optimum pore structure, the next step would be to optimize the chemical formulation and composition of the catalyst.
Patents which deal with variations in the chemical composition and formulation are as follows: U.S. Pat. No. 3,898,155, U.S. Pat. No. 3,931,052, U.S. Pat. No. 3,985,684, U.S. Pat. No. 4,344,867 and G.B. Pat. No. 2,032,795. The first three patents consider the inclusion of a third element besides the Group VIB and Group VIII elements in the catalyst. U.S. Pat. No. 4,344,867 is concerned with a chemical treatment of a catalyst support. The G.B. Pat. No. 2,032,795 patent eliminates the Group VIB element from the composition and introduces a method of core impregnation for the preparation of the catalyst. All of these patents however are based on the fact that larger pores can accumulate higher amounts of metals. Thus, while some improvement in demetallization may be accomplished employing these catalyst, the increase in demetallization is generally accompanied by a loss in hydrogenation activity.
Accordingly, it is the principal object of the present invention to provide a catalyst and method for making same which exhibits good simultaneous demetallization and hydrogenation activity when processing heavy hydrocarbon feeds.
It is a particular object of the present invention to provide a catalyst and method for making same as set forth above having two distinct metal phases deposited on a refractory support.
It is a further object of the present invention to provide a catalyst and method for making same as set forth above wherein the first phase is a demetallization phase and the second phase is a hydrogenation phase.
It is a still further object of the present invention to provide a catalyst and method for making same as set forth wherein the weight ratio of the phases as measured by mossbauer spectrum are controlled.
Further objects and advantages of the present invention will appear hereinbelow.